1. Field of the Invention
The present invention relates to the characterization of blood types and blood components, and, more particularly, to the spectrophotometric characterization of blood types and blood components.
2. Description of Related Art
Current technology for blood typing or for the diagnosis of pathogens requires analysis by microscopy and/or immunoassay techniques. Specifically, for blood typing, an agglutination reaction is typically used that results from the association of specific antibodies with antigens present on the erythrocyte (red blood cell) surface. The disadvantages of this procedure are that it requires significant amounts of time, trained individuals, and well-equipped laboratory facilities. For blood typing, for instance, an involved laboratory procedure is needed to detect the cell surface antigens. (See, for example, the Technical Manual of the American Association of Blood Banks, Bethesda, Md., 1996.)
In a particular method, an instrument such as that made by Olympus (for example, Model PK-7200, Olympus, Lake Success, N.Y.) is used to detect light obfuscation in agglutinated blood samples to which commercial monoclonal antibodies have been added.
The presence of weak antigens (e.g., weak D) may only be detected by an indirect antiglobulin procedure after incubation of the test red cells with anti-D.
A reliable test for platelet viability does not exist at present. Typically platelet-rich plasma units are discarded after 5 days, and/or pH measurements, which must be performed by invading the storage container, are made (pH decreases with storage time owing to continued metabolism). Visual inspection is also performed, with a “shimmering” indicating the presence of viable, discoid-shaped platelets, although this is obviously not a quantitative measure of viability.
Bacterial contamination is another factor that is of concern in blood product storage, leading to the discarding of units after a predetermined time (e.g., 5 days for platelets). The danger of contamination results from the storage of platelet units at room temperature to maintain viability. Storage at this temperature, however, can lead to bacterial contamination, leading to infection upon infusion into a patient. At present the only reliable method for detection of such contamination is aerobic and anaerobic culturing, with visual detection of bacterial colonies.
Platelet cross-matching is recommended for patients who are refractory to routine platelet transfusions, such as those with hematologic disorders, those with viral infections, or those who have experienced alloimmunization through pregnancy or transfusion. A method known for antibody detection is a solid-phase system (Capture-P, Immucor, Inc., Norcross, Ga.). This system requires a multiplicity of steps, including transferring samples to microtitration wells, centrifugation, washing, agitation, incubation, and further centrifugation.
Cell component counting is another important characterization protocol. White blood cells, for example, can be difficult to count if they are present in small numbers. At present automated hematology analyzers that employ light scattering techniques are used, but these can introduce a high error when determining counts for low sample numbers. In cases of leukoreduced blood products with lower numbers of white blood cells, staining and microscopy or flow cytometry are typically used.
Another limitation of the currently employed technology is a lack of on-line capability for the characterization of blood components, as well as a lack of portable instrumentation capable of detecting, counting, and classifying specific blood components. The problem of portable instrumentation and suitable methods of analysis and diagnosis is particularly relevant to the medical industry, where the need for rapid analysis and diagnosis often involves life-threatening situations. Although the analytical instrumentation used in medical and clinical laboratories has improved considerably over the past decade, there are still no suitable techniques capable of detecting, classifying, and counting on-line critical cell populations and/or pathogens in blood and other bodily fluids. Typically the particles of interest have sizes ranging between 0.5 and 20 μm, and, in many instances, are present in fairly dilute concentrations.
As is known from spectroscopy theory, a measure of the absorption of a solution is the extinction coefficient, which also provides a measure of the turbidity and transmission properties of a sample. Spectra in the visible region of the electromagnetic spectrum reflect the presence of certain metal ions, complexes, and molecules with extensive conjugated aromatic structures. In the near-uv region small conjugated ring systems affect absorption properties. However, suspensions of very large particles are powerful scatterers of radiation, and in the case of microorganisms, the light scattering effect is sufficiently strong to mask or distort absorption effects. It is therefore known to use uv/vis spectroscopy to monitor purity, concentration, and reaction rates of such large particles.
Many attempts have been made to estimate the particle size distribution (PSD) and the chemical composition of suspended particles using optical spectral extinction (transmission) measurements. However, previously used techniques require that either the form of the PSD be known a priori or that the shape of the PSD be assumed. One of the present inventors has applied standard regularization techniques to the solution of the transmission equation and has demonstrated correct PSDs of a large variety of polymer lattices, protein aggregates, silicon dioxide particles, and microorganisms.
It is also possible to use the complementary information available from simultaneous absorption and light scattering measurements at multiple angles for the characterization of the composition and molecular weight of macromolecules (Garcia-Rubio, 1993; and “Multiangle, Multiwavelength Particle Characterization System and Method,” U.S. patent application Ser. No. 08/489,940, filed Jun. 13, 1995, now abandoned, and continuation application thereto U.S. patent application Ser. No. 08/780,828, filed Jan. 10, 1997, now U.S. Pat. No. 5,808,738, the disclosures of which are incorporated herein by reference).